A 3-yr study was conducted in California’s southern San Joaquin Valley to determine the overwintering survival of the corn leafhopper, Dalbulus maidis (DeLong and Wolcott), and the mollicute, Spiroplasma kunkelii, the causal agent of corn stunt disease. Corn leafhopper populations were sampled from November to March using yellow sticky cards, D-vac suction samples, and inspection of volunteer corn plants and spring planted corn. S. kunkelii presence was determined by sampling sentinel plants placed in the field during the winter, leafhoppers collected throughout the winter, and evaluation of volunteer plants over the winter and spring planted corn. Leafhoppers were collected on yellow sticky cards throughout the winter during all 3 yr. They were also regularly recovered from alfalfa, Medicago sativa L., winter forage (wheat, Triticum aestivum L., and triticale, Triticale hexaploide Lart. and riparian areas by D-vac suction sampling. Females constituted the majority of leafhoppers (>80%) recovered on both sticky cards and from D-vac samples. S. kunkelii was recovered from leafhoppers throughout the winter, from sentinel plants, and in spring planted corn. Volunteer plants were determined to be a critical key in leafhopper overwintering, and consequently, the survival of S. kunkelii. Volunteers extended the season by as much as 2 mo, thus shortening the period of time the leafhoppers were forced to go without a food source. The possible reasons for a shift in the leafhopper from cyclic pest to persistent pest in the region are also discussed.